The present invention relates to a new and improved constructon of a gas-blast switch.
The gas-blast switch of the invention is of the type comprising a gas tight insulating housing within which there is arranged a fixed contact surrounded by a blast chamber and a movable contact as well as a blast nozzle movable along with the movable contact and connected with a pump device. The pump device comprises a pump cylinder movable together with the movable contact. This pump cylinder is displaceable upon a stationary piston. Means are coupled with the pump cylinder and are impinged, during the course of the cut-off stroke of the gas-blast switch by the pressurized gas heated by the arc, in order to augment the pump stroke of the pump device.
A heretofore known gas-blast switch of this type, as disclosed in FIGS. 3a to 3c of West German patent publication No. 2,620,675, is constructed in the following manner. The pump cylinder is structured as a thin wall extension of the blast nozzle at the inlet side. This blast nozzle is closed in the cut-on or switching-on position by the fixed contact and thus in conjunction therewith forms the floor of the pump cylinder. The movable contact constructed as a continuous open tube is coaxially arranged internally of the thin wall projection or extension of the blast nozzle and fixed thereto by means of struts, so that between the extension or projection and the movable contact there remains free a jacket space or compartment forming the pump chamber. Engaging into this pump chamber at its one side is the stationarily supported pump piston which centrally has a throughpassage for the movable contact. At the end of the extension of the blast nozzle there is attached a further cylinder havng a larger internal diameter and which is displaceable upon a flange formed at the other side of the pump piston and radially protruding therefrom.
Now if during the cut-off movement the movable contact and together therewith the blast nozzle and the pump cylinder along with the further cylinder are moved away from the fixed contact element, then initially the movable contact disengages from the fixed contact, thereby drawing an arc, and at the same time the pump piston displaces extinguishing gas out of the pump chamber. The extinguishing or quenching gas blows the arc and initially can only escape through the movable contact element into the further cyllinder within which there thus occurs a pressure increase augmenting the cut-off movement. However, as soon as during the course of the cut-off movement the blast nozzle is also freed by the fixed contact, then not only does the extinguishing gas, expelled out of the pump chamber, no longer flow through the movable contact into the further cylinder, but the heated extinguishing gas collected therein at increased pressure again expands over the movable contact. Both gas streams, namely that of the fresh extinguishing gas emanating from the pump chamber and that of the immediately prior so-to-speak "contaminated" extinguishing gas emanating from the further cylinder now flow by means of the blast nozzle into the blast chamber. However, as a result thereof there also is interrupted the previous assistance of the cut-off movement, i.e., the drive brought about by the heated extinguishing gas, and furthermore, the arc is also blown with gas which just previously already has blown the arc and therefore its original extinguishing and cooling properties have been temporarily impaired.